An integrated circuit (IC) is an electronic circuit formed on a small piece of semiconducting material, typically silicon. ICs are used in virtually all electronic equipment today and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances, which are made possible by the low cost of ICs, are now inextricable parts of modern societies. ICs can be made very compact, having up to several billion transistors and other electronic components on a piece of semiconducting material about the size of a fingernail. Feature sizes of ICs, such as the width of each conducting line, are made smaller and smaller for successive generations of technology. For example, in 2008 the width of each conducting line dropped below 100 nanometers and in 2013 is in the tens of nanometers.
Despite the ever shrinking feature size for successive technology nodes, the overall power consumption per unit area has remained the same or even tended to increase for successive technology nodes. This is because of the increased density at which devices are packed on the ICs and because of the higher operating frequencies for the newer devices. To help curtail this increase in power consumption between successive technology nodes, newer technology nodes typically utilize lower supply voltages than previous technology nodes. For example, whereas a typical IC made according to a 0.6 μm technology node was powered with a 5 volt DC supply, more recent ICs at the 0.13 μm technology node are powered with a 1.2 volt DC supply. As supply voltages have decreased, the voltage drop which can be tolerated between the supply rails has also decreased. For example, if a 5% supply rail drop is tolerable, a 5 V supply could tolerate a 250 mV voltage drop, but a 1.2 V supply can tolerate only a 60 mV drop. Thus, for modern technology nodes where supply voltages are decreasing, it is becoming more and more important to accurately model supply rail voltages.